The present invention relates to a heat transfer sheet used in heat transfer printers, a method for producing the heat transfer sheet and heat transfer method and, in particular, to a heat transfer sheet high in recording sensitivity and high in maximum recording density, a method for producing the heat transfer sheet and a heat transfer method.
Recently, heat transfer printers have been widely used as printers for making hard copies of images formed on various displays.
As recording material used in the printers, a heat transfer sheet and a recording sheet are used.
This heat transfer sheet comprises a substrate and, provided thereon, an ink layer containing a dye which transfers onto a recording sheet by sublimation, evaporation or diffusion with application of heat. (This dye is hereinafter referred to as "sublimating dye".) Furthermore, this heat transfer sheet has the feature that transfer (recording) density (transfer quantity of dye and reflection density of print image) can be easily controlled by intensity of heat energy applied without deterioration of resolution.
Many examples of such heat transfer sheet are disclosed in Japanese Patent Kokai (Laid-Open) No. 60-101087 and others. As dyes used for this heat transfer sheet, disperse dyes which have been used in heat transfer printing are used. Japanese Patent Kokai (Laid-Open) No. 59-199295 and 60-27594 in addition to the above patent publication show examples of using such dyes.
Specific examples of these dyes are mentioned in Japanese Patent Kokai (Laid-Open) Nos. 61-148096, 61-163895 and 60-53564.
In the above conventional techniques, sufficient consideration has not been given to transfer of dye to a recording sheet, namely, density of image (reflection density) on the recording sheet at formation of image by transfer, i.e., recording sensitivity and maximum attainable recording (reflection) density.
As a result, as compared with heat-melt type heat transfer sheet in which an ink layer is molten or softened with heat and transfers to a recording sheet, the above-mentioned heat transfer sheet of sublimation type suffers from the problems that it requires much heat energy for transfer and long time for recording and contrast of resulting image is low.